As disclosed in JP2012-146621A, for example, an illumination device using a coherent light source is widely used. A laser light source that oscillates a laser light (laser beam) is typically used as the coherent light source.
JP2012-146621A discloses a vehicle lighting tool. The vehicle lighting tool includes a light source, which can be formed by a laser oscillation device, and four hologram devices. The respective hologram devices are moved by a rotary driving apparatus to be located on positions where they can receive a laser light from the light source. The respective hologram devices diffract the laser light to achieve illumination in a desired light distribution pattern. By suitably selecting a hologram device which is irradiated with a laser light, illumination in a predetermined light distribution pattern can be achieved. In order to achieve illumination in a great number of light distribution patterns by using this vehicle lighting tool, it is necessary to increase the number of hologram devices that can be selectively irradiated with a laser light. In this case, the structure and control of the device become significantly complicated. Further, while it is necessary to ensure light paths of incident light and emergent light for each hologram device, the number of hologram devices that are rotatably supported about one axis has an upper limit. Namely, the illumination device (lighting tool) disclosed in JP2012-146621A is difficult to perform illumination in a great number of light distribution patterns.